This invention relates to an antenna material for use as an antenna reflector and has particular utility for large antennas in outer space. It is well known that antenna reflectors up to a kilometer in diameter will be needed for the coming generation of spacecraft and space platforms. Unfortunately, the requirements for dimensional stability of the antenna shape become more stringent as the antenna size or frequency increases in order to prevent degradation of antenna performance.
One of the principal causes of antenna shape distortion is thermal expansion and contraction. Antenna materials exposed to direct sunlight reach temperatures of 100.degree. C. or more but these temperatures will then decrease to -180.degree. C. or less when the material is shaded. Such thermal excursions are normal in the space environment and they cause radical changes in the shape and performance of antenna reflectors made from common materials.
The reflective surface of spacecraft antennas is often constructed of woven or knitted wires or metallized polymeric yarns. An open mesh type of structure achieves a low mass/area ratio and reduces overall antenna weight. Mesh materials which have been used on spacecraft antennas include gold plated molybdenum wire and copper coated polyester yarns. While these materials have been satisfactory for parabolic antennas up to 9 meters in diameter, their coefficient of thermal expansion (CTE) is excessive for the coming generation of very large antennas. The CTE of molybdenum and polyester is 9.times.10.sup.-6 /.degree. C. and 60.times.10.sup.-6 /.degree. C. respectively.
In addition to being lightweight and strong, other requirements for antenna mesh are good flexibility and durability. Antennas are stowed in a swell volume container and then deployed in space. Stowage causes sharp bends and high crush loads on the fabric which can cause work-hardening and kinking of metal fibers and debonding of metal coatings from polymeric yarns. Both metal and polymer yarns stretch under load by the phenomena called creep. Polymeric yarns lose strength and become brittle with age, and the process is accelerated if cracks in the metal coating expose the yarn to ultraviolet radiation from the sun. Other disadvantages of polymer yarns include low thermal stability and moisture absorption/desoprtion which affects dimensions during terrestrial handling. There is a definite need for antenna materials with improved durability and dimensional stability.